History relearned and improved: flyash mortars are making a national appearance. (the...

Yogi Berra, in describing a particularly strange event, once said "It's deja vu, all over again." Whether he meant it or not, this famous quote has been proven correct many times over. So with a historical tradition that dates to that of ancient Rome, it shouldn't be too unexpected for masons

Masonry cement using pozzolans as its major component isn't something new. Masons in Texas and other portions of the Southwest have been using mortars and stucco featuring high quality formulations of hydrated lime, portland cement, high performance pozzolans, and other additives for years. But recently masons working in other areas of the country began learning about the positive working characteristics of these products.

As manufacturers develop new efficient processing operations, the spread of mortar cements using pozzolans is spreading. For example, masons recently finished a school building (right) in a suburb of Atlanta with this material, and more are planned for this year.

Often referred to as masonry cements, the jobsite and final construction properties of the products are well documented. These products have been subjected to extensive tests and the results indicated that they perform beyond the minimum performance specification required by national code and standards setting organizations.

Specifically these products exhibit high compressive strengths. In fact, due to their unique ingredients, the ultimate strengths of these products are often double the standard requirement.

Because of their formulation these type of mortars also tend to have higher bond strengths than traditional products. One manufacturer claims that due to the special formulations, 88% of the cementitious material contribute to bond strength. This figure is compared to traditional mortars where the amount is closer to 50%.

And finally there's the fact that pozzolan-based mortars perform well in preventing water penetration. Manufacturers have tested brick walls built with these products and subjected the units to the Hurricane test (ASTM E-514). They report that there is insignificant leaking even after 24-hours. Brick walls built with traditional mortars subjected to the same test may leak anywhere from 8 to 60 gallons of water per hour.

In the field

Masons laying block with masonry cements comprised of pozzolanic materials as their prime ingredients usually have little need to alter their work routine. They perform in much the same way as portland cement-based mortars. These products often increase mason productivity, according to field reports from many contractors.

When properly mixed, the mortar has a creamy texture. The material bonds well and has a longer than traditional set time. Since the mortar remains so well-formed longer, the mason doesn't have to stop and tool so often. This feature allows the mason to work in longer paths, which increases productivity. And since the product is so supple, masons report that they are their able to place better head joints.

These products have developed a good reputation in regards to their longer board life. They require little water if retempering becomes necessary. The result is a mortar that keeps its strength better, has good workability after retempering, and increases productivity.

One practice that masons and laborers should be concerned about is proper mixing. While material proportions of three parts loose, damp masonry sand to one part cement is consistent with traditional practices, care must be used when adding water. Because of the reduced need for mixing water, pozzolanic cements often require less mixing water.

To learn more about pozzolanic mortars and stucco, please contact the following manufacturers:

Best Masonry, a division of ISG Resources, circle 1

Mineral Resource Technologies, circle 2